This invention relates to apparatus for use in the internal examination of pipes and, more particularly, to the x-ray examination of welded joints in cylindrical pipes. The device of the present invention is particularly useful in the x-ray examination of welds in shorter pipe sections during shop fabrication, as opposed to field inspection of welds in relatively longer pipeline sections.
Radiographic inspection devices for use in examining circumferential welds from the inside of cylindrical pipes are well known in the art. Such devices vary widely in complexity from self-propelled, fully automatic equipment to manually-operated, relatively simple devices. Irrespective of their complexity, the devices of the prior art may be classified in two basic types.
One type utilizes a series of circumferentially spaced wheels which are biased against the interior cylindrical pipe surface to inherently maintain the radiographic device on the centerline of the pipe as it travels therein. A fully automated version of a device of this kind is shown in U.S. Pat. No. 4,006,359. A similar type of device is disclosed in U.S. Pat. No. 3,492,477 and, like the apparatus shown in the previously identified patent, this device is primarily intended for use in relatively long pipeline sections. These devices are, however, far too complex for use during shop fabrication of welded pipe sections. A manually operated version of the same type of inspection device is shown in U.S. Pat. No. 2,607,012. Because this device requires operator access from outside the pipe, its use is necessarily restricted to relatively shorter pipe sections. However, even this device is too cumbersome for rapid installation and operation in the x-ray inspection of one or more welds in a relatively short pipe section.
The other general type of prior art device comprises a wheeled carriage adapted to travel along the bottom of a pipe interior. Typical prior art embodiments of this kind are shown in U.S. Pat. Nos. 3,547,040 and 3,949,227. Complex pendulum-controlled steering mechanisms are used to overcome the tendency of these devices to climb the pipe walls during longitudinal movement through the pipe and to maintain carriage travel along the bottom of the pipe. Though possibly suitable for use in longer pipelines, these devices are also too complex for the rapid inspection of welds, particularly in a shop environment during the fabrication of short sections.
Thus, the prior art discloses no device which is simple, reliable and easy to use for the rapid x-ray examination of a few welds in a relatively short section of pipe. Further, there exists a need for a device which is readily adaptable for use in pipes of varying diameters and ranges of wall thicknesses for each diameter.